Control of crystal orientation and continuous growth throughinclination of coaxial nozzle in laser powder deposition ofsingle-crystal superalloy

Zhaoyang Liu,Huan Qi, Liang Jiang

Keywords: Laser powder deposition， Crystal growth， Single-crystal superalloy

Abstract: The effects of inclining angle of the coaxial nozzle in the longitudinal section of deposited bead on themolten pool geometry and the corresponding crystal growth in laser powder deposition of single-crystalsuperalloy are studied through the coupling of a numerical FLUENT program and a three-dimensionaltransient transport phenomena mathematical model. Systematical experiments with single-crystalnickel-based superalloy were conducted to verify the computational results. The results show that theinclination angle of the coaxial nozzle in the longitudinal section of deposited bead has a predomi-nant effect on the molten pool geometry and the solidified microstructure. The inclination of coaxialnozzle reduces the height of the molten pool while increases the melting depth compared to the normal-direction deposition. The epitaxial grain growth in the deposited bead is enhanced when the coaxialnozzle inclines toward the laser scanning direction, while it is restrained as the nozzle inclines towardthe opposite direction. When the coaxial nozzle inclines to a +45◦, the ratio of melting depth to the heightof equiaxied stray grain on the top of the previous layer of deposited bead exceeds 1.0, which impliesthat the deposited layer can completely remelt the stray grains in the previous layer. The capacity ofcontinuous-epitaxial grain growth can be therefore achieved through the nozzle inclination effectively.This method can be used to optimize and control the processing parameters and broaden the processingwindow for a single-crystal turbine blade tip repair.